1. Field of the Invention
The present invention relates to musical tone synthesizing apparatuses, and more particularly, to musical tone synthesizing apparatuses applicable to synthesis of the sound of stringed instruments, especially plucked or percussive stringed instruments.
2. Prior Art
Various musical tone generating apparatuses are conventionally known, wherein the sound of one or more conventional, non-electronic musical instruments is synthesized through simulation of the mechanism of sound generation for each target instrument.
Examples of this type of apparatus include that disclosed in Japanese Patent Application, First Publication No. Sho-63-40199 and that disclosed in Japanese Patent Application, Second Publication No. Sho-58-58679, both of which are apparatuses which simulate the mechanism, and in this way synthesize the sound of plucked or percussive stringed instruments. Typically, these apparatuses include one or more closed loop circuits wherein the action of a vibrating string is simulated. Additionally, an excitation signal generating circuit is provided from which an excitation signal can be input into the closed loop circuit, and which acts to simulate the input of mechanical energy into a string of the conventional instrument, that is, the excitation signal generating circuit simulates the plucking or striking of a string in a plucked or percussive stringed instrument, respectively.
The above described closed loop circuit incorporates a low-pass filter and delay circuit in serial. The low-pass filter simulates acoustical losses which occur in a vibrating string following plucking or striking thereof, in other words, the time decay in amplitude of vibration, and hence of mechanical energy, in the vibrating string. The delay circuit acts to simulate the propagation delay imparted to waves traveling back and forth along the length of the string.
As mentioned above, the excitation signal generating circuit simulates the input of mechanical energy into a string of a stringed instrument. To do so, the excitation signal generating circuit injects an excitation signal, for example, an impulse signal into the closed loop circuit which then proceeds to circulate repeatedly therearound, the rate of circulation dependent on the characteristics of the above mentioned delay circuit, the energy of the circulating signal decaying with time at a rate dependent on the characteristics of the above mentioned low-pass filter. After the excitation signal has been input into the closed loop circuit, the circulating signal is sampled, thereby obtaining an output signal which represents the simulated sound of the target instrument.
With conventional stringed instruments, a damping operation is often applied to one or more of the vibrating strings during a performance. Depending on the technique employed by the performer as expressed by rate and intensity of damping, the vibration of a string and hence the sound produced thereby can be caused to gradually fade away or to suddenly stop. In the case of a conventional piano, each key is provided with a dedicated damping mechanism which includes a felt covered damping block which is brought into contact with the corresponding string or strings when the key is released, assuming that the sustain pedal is not depressed.
Aside from the piano or harpsichord, most other stringed instruments do not included a dedicated damping mechanism, for which reason musicians generally apply one of various manual damping techniques when it is desired to terminate the sound generation of one or more strings, or when a decrescendo effect is desired. Most often, these techniques involve pressing a finger or hand against the corresponding strings with a variable degree of pressure.
In the case of a guitar, when it is desired to damp all of the strings, a right handed player will most often press the ulnar aspect of his/her right hand against the strings in proximity to the bridge of the guitar, or alternately, the shaft of his/her left thumb at a position over the fretboard. When it is desired to selectively damp one or more strings, for open strings, the right handed player will generally apply the tip of one of the left fingers or thumb to each string to be damped. Additionally, for strings not open, damping can be effected by partially or completely releasing the finger which is holding a string against the fretboard.
In the case of electronic apparatuses which simulate the sound of conventional stringed instruments, none of the conventionally known apparatuses incorporate a means for simulation of controlled damping as described above. Ordinarily, in order to attenuate or stop the simulated tone corresponding to a vibrating string, these apparatuses incorporate a variable gain amplifier/attenuator circuit within the closed loop circuit. By this means, the amplitude of the generated signal can be caused to diminish gradually, or to terminate suddenly. Finely controlled damping as employed by musicians playing conventional stringed instruments, however, is generally not possible with these conventional apparatuses. Consequently, the ability to synthesize fully natural sounding musical tones is compromised with the result that music produced by such apparatuses tends to sound unrealistic.